What subnet ID / prefix value should I use for my OpenFabrics networks?
You can use any subnet ID / prefix value that you want. However, Open MPI v1.1 and v1.2 both require that every physically separate OFA subnet that is used between connected MPI processes must have different subnet ID values. For example, if you have two hosts (A and B) and each of these hosts has two ports (A1, A2, B1, and B2). If A1 and B1 are connected to Switch1, and A2 and B2 are connected to Switch2, and Switch1 and Switch2 are not reachable from each other, then these two switches must be on subnets with different ID values. See this FAQ entry for instructions on how to set the subnet ID. 31. How do I set my subnet ID? It depends on what Subnet Manager (SM) you are using. Note that changing the subnet ID will likely kill any jobs currently running on the fabric! • OpenSM: The SM contained in the OpenFabrics Enterprise Distribution (OFED) is called OpenSM. The instructions below pertain to OFED v1.2 and beyond; they may or may not work with earlier versions. • Stop any OpenSM ins
